Use of fluorinated liquids

ABSTRACT

Use of one or more fluorinated liquids as dielectric working fluids in plants or heat transfer circuits comprising parts formed by polymer compound in contact with said fluids, said fluorinated liquids having:  
     boiling point in the range 50° C.-250° C.,  
     formula 
     R′-R f -R  (I) 
     wherein:  
     R, R f  and R′ are as defined in the description.

[0001] The present invention relates to the use of fluorinated compoundsliquid at room temperature, as dielectric working fluids in plants orcircuits comprising parts formed by organic polymer material in contactwith said working fluids or fluorinated liquids.

[0002] Specifically the invention compounds show an improved propertycombination compared with the known working fluids of the prior art orindustrially used, as indicated hereafter:

[0003] reduced permeability and swelling of the polymer compounds withwhich they are in contact;

[0004] capability to dissipate the electrostatic charges generated bytriboelectric effect when they come into contact with non conductivepolymer compounds.

[0005] It is well known that dielectric fluids are fluids which act aselectric insulator, or such that an electric field can be maintainedtherein with a minimum dissipation of power.

[0006] As known, in the manufacture of equipments used in the chemical,pharmaceutical industry, of the heat exchangers (refrigeration), and inparticular in the electric and electronic industry, organic polymercompounds, both plastomeric and elastomeric, are used in substitution ofmetals. Depending on the parts of the plant, fluorinated or hydrogenatedpolymer compounds can be used. In the parts subjected to thermal ormechanical stress, such for example in the pipe bundles of heatexchanger, fluorinated compounds are generally used. Other parts of theplant, for example, gaskets, O-ring, are made by hydrogenated or(per)fluorinated elastomeric compounds.

[0007] The substitution of metals with polymer compounds in plants andcircuits used in the industry allows to obtain various advantages amongwhich, for example, the removal from the working fluid of the metalparticulate which forms due to the particle separation from the weldingpoints, for example of the pipe bundles, and from the bent parts orconnections of equipments particularly subjected to mechanical stresses.The metal particulate circulating with the working fluid can compromisethe plant functionality, for example obstructing the flow regulationvalves. Or it can compromise the dielectric properties of the workingfluid, which are critical in the plants used in the electronic semiconindustry.

[0008] Even though the use of polymer compounds in plants has favouredthe solution of various problems, it is known that the compounds used inthe prior art as working fluids can in the time compromise theproperties of the organic polymer compound with which they are incontact.

[0009] The most significant drawbacks are the following:

[0010] (1) swelling of polymer parts with consequent loss of themechanical properties of the manufactured article;

[0011] (2) permeation of the fluid through the compound, making itnecessary the monitoring of the amount of fluid circulating in the plantto refill the losses;

[0012] (3) when the used polymer compounds are not conductive, anaccumulation of electrostatic charges takes place on the manufacturedarticle owing to the triboelectric effect if the working fluid hasdielectric properties; under these conditions electric discharges cantake place, even of an entity such to perforate the polymer material.

[0013] Said drawbacks compromise the plant efficiency and safety.

[0014] For said reasons in the plant construction for example of heattransfers, the choice of the suitable combination polymercompound—working fluid results critical, considering the width of thethermal cycle and the possible state transformations to which the fluidis subjected during its use.

[0015] In the prior art processes to dissipate electrostatic charges aredescribed. For example in U.S. Pat. No. 3,907,955 a process to dissipateelectrostatic charges, generated by the flow of fluids at high speed incircuits which are used in the aeronautic sector is described. Accordingto the process of said patent the polymer compound used to manufacturethe circuits (PTFE) is made conductive by the addition of graphite. Saidaddition shows the drawback that if a dielectric working fluid is usedin the plant, it can be polluted by conductive particulate coming fromthe graphite used in the preparation of pipes and therefore lose theinsulating properties. The same drawback takes place by usingelastomeric compounds, which as well known are charged with fillers to .confer mechanical properties. Also in this case the fillers during theuse are extracted from the working fluid.

[0016] The need was felt to have available a dielectric working fluid,to be used in industrial circuits or plants, for example heat transfers,comprising parts made by polymer material, showing the followingimproved combination of properties:

[0017] reduced permeability,

[0018] reduced swelling,

[0019] good dissipation of electrostatic charges.

[0020] The Applicant has surprisingly and unexpectedly found compoundsusable as dielectric working fluids, liquid at room temperature, whichsolve the above technical problem.

[0021] An object of the invention is the use of one or more fluorinatedcompounds, liquid at room temperature, as dielectric working fluids inplants or heat transfer circuits comprising parts formed by polymercompound in contact with said fluids, said liquids having boiling pointin the range 50° C.-250° C., preferably 70° C.-200° C., and havingformula

R′-R_(f)-R  (I)

[0022] wherein:

[0023] R′ is —(O)_(n0)—C_(n)F_(2n)H, n being an integer from 1 to 4,preferably 1 or 2; n0 is equal to 0, 1;

[0024] R is: —C_(n)F_(2n)H, —C_(m)F_(2m+1); wherein

[0025] in the end groups R, R′ one fluorine atom is optionallysubstituted with one chlorine atom; n in R is as defined in R′; m is aninteger from 1 to 3;

[0026] R_(f) is:

[0027] linear or branched perfluoroalkylene from 2 to 12 carbon atoms,containing at least one ether oxygen atom, when R_(f) has said meaningn0 in R′ is preferably equal to zero;

[0028] perfluoropolyoxyalkylene comprising units statisticallydistributed along the chain, selected from the following:

[0029] (CFXO) wherein X=F or CF₃;

[0030] (CF₂(CF₂)_(d)O) wherein d is an integer comprised between 1 and3;

[0031] (C₃F₆O);

[0032]  when R_(f) is perfluoropolyoxyalkylene n0 in R′ is preferablyequal to 1.

[0033] The unit (C₃F₆O) in R_(f) has the following meanings:

[0034] (CF₂CF(CF₃)O), (CF(CF₃)CF₂O).

[0035] Preferably in formula (I) R is a group selected from thefollowing: —CF₂H, —CF₂CF₂H, —CFHCF₃.

[0036] The working fluids, the above described compounds of formula (I),generally have a number average molecular weight from 200 to 800.

[0037] In the fluids of the invention of formula (I) preferablyR_(f)=(per)fluoropolyether chain with n0 of R′ equal to 1, R_(f)preferably has one of the following structures:

[0038] 1) —(CF₂O)_(a)—(CF₂CF₂O)_(b)—

[0039] when a is different from zero, then b/a is comprised between 0.3and 10, extremes included; when a is equal to zero b is an integer asdefined below;

[0040] R in formula (I)=—C_(n)F_(2n)H;

[0041] 2) —(CF₂—(CF₂)_(z′)—CF₂O)_(b′)—

[0042] wherein z′ is an integer equal to 1 or 2; b′ is as defined below;

[0043] 3) —(C₃F₆O)_(r)—(C₂F₄O)_(b)—(CFL₀O)_(t)—

[0044] L₀=—F, —CF₃;

[0045] when b and t are different from zero r/b=0.5-2.0; (r+b)/t=10-30and all the units with r, b and t indexes are present;

[0046] or b=t=0 and r satisfy the proviso indicated below;

[0047] or b=0 and r and t are different from zero; a, b, b′, r, t, areintegers such that, or whose sum is such that the compound of formula(I) containing the bivalent radical R_(f) has a boiling point in theabove range.

[0048] The dielectric fluids, or compounds of the invention, can be forexample the following:

[0049] HCF₂O(CF₂CF₂O)_(1.8)(CF₂O)_(1.4)CF₂H;

[0050] HCF₂O(CF₂CF₂O)₂(CF₂O)_(0.7)CF₂H;

[0051] HCF₂O(CF₂CF₂O)₃(CF₂O)_(0.4)CF₂H;

[0052] HCF₂O(CF₂CF₂O)₃(CF₂O)_(1.6)CF₂H;

[0053] HCF₂O(CF₂CF₂O)₄(CF₂O)_(0.9)CF₂H;

[0054] CF₃O(CF₂CF₂O)₂CF₂H;

[0055] CF₃O(CF₂CF₂O)₂(CF₂O)CF₂H;

[0056] CF₃O(CF₂CF(CF₃)O)₂CF₂H;

[0057] CF₃O(CF₂CF(CF₃)O)₃CF₂H;

[0058] CF₃O(C₃F₆O)₂(CF(CF₃)O)CF₂H;

[0059] HCF₂CF₂O(CF₂CF₂O)CF₂CF₂H;

[0060] HCF₂CF₂OCF₂C(CF₃)₂OCF₂CF₂CF2H;

[0061] CF₃(CF₂)₅OCF₂CF₂H;

[0062] CF₃(CF₂)₆OCF₂H;

[0063] C₅F₁₁OC₅F₁₀H.

[0064] Preferably the used compounds are the following:

[0065] HCF₂O(CF₂CF₂O)₃(CF₂O)_(0.4)CF₂H;

[0066] HCF₂O(CF₂CF₂O)_(1.8)(CF₂O)_(0.4)CF₂H.

[0067] As said, according to the present invention the fluorinatedliquids can be mixtures of the compounds of formula (I).

[0068] The fluorinated dielectric fluids can be prepared according tothe methods described in U.S. Pat. No. 3,704,214, U.S. Pat. No.3,715,378, patent application WO 95/32174 and U.S. Pat. No. 5,969,192.

[0069] As said the invention compounds show an optimal combination oflow permeability and swelling in polymer compounds and capability todisperse the electrostatic charges present when the polymer compoundsare not conductive.

[0070] It has resulted surprising and unexpected that the inventioncompounds show said improved combination of properties, sincehydrofluoroethers containing in the molecule a perfluoroalkyl radicallinked to a hydrogenated alkoxy group, for example —OCH₃, —OC₂H₅, givepermeation values higher than or equal to the double in polymercompounds compared with the invention compounds having about the sameboiling point. Besides, also the swelling is higher by using the abovehydrofluoroether fluids of the prior art (see the Examples).

[0071] As said, the dielectric fluids of the present invention,compounds of formula (I) or mixtures thereof, can be used in plants orheat transfer circuits comprising parts formed by plastomeric andelastomeric polymer compounds, both fluorinated and hydrogenated. Theproperties of the fluids of the present invention allow their use evenwith non conductive polymer compounds. For example as polymer compoundsfor said circuits or plants, polymers or copolymers oftetrafluoroethylene and of vinylidene fluoride; polymers and copolymersof ethylene and propylene, EPDM, silicone rubbers, can be used.

[0072] The fluids of the present invention do not need the addition ofantistatic agents since even though they are dielectric, it has beenfound that they are capable to disperse the electrostatic chargespresent in non conductive polymer compounds. This result is unexpectedsince perfluoropolyether compounds used as dielectric working fluids inheat transfer circuits are unable to disperse the electrostatic charges.This is the drawback shown by said working fluids commercially wellknown in said application.

[0073] The use according to the present invention is carried out bymaking the circuit or the plant to work by circulation in the pipes ofthe above fluorinated liquids.

[0074] The fluids of the present invention are not flammable, have ODP(ozone depletion potential) zero, low GWP (global warming potential) andreduced residence times in the atmosphere.

[0075] Some illustrative Examples follow which are not limitative of thepresent invention.

EXAMPLES

[0076] Triboelectric Measurements

[0077] The determination is carried out by using an equipment consistingof a fluid tank, a circulating pump with flow regulation valve and 1metre long PTFE pipe having diameter of 8 mm. The flow rate is 300litres/h. The flow regulation valve must allow a continuous flowing ofthe tested fluid through the PTFE pipe. The tank is filled with thetested fluid. By means of a voltmeter placed at a definite distance fromthe PTFE pipe the electrostatic charge is determined on the pipe at zerotime and subsequently at determined intervals during the fluid flowing.

[0078] The obtained result is expressed in per cent ratio between thecharge determined on the pipe at the considered time and that determinedat the starting of the test.

[0079] Permeability Measurements

[0080] The fluid permeability has been determined by the followinggravimetric methods:

[0081] Method I

[0082] In a cup having diameter of 5 cm, 50 cc of the tested fluid areintroduced. A polymer plaque of which one wishes to determine thepermeability to fluid, compression moulded having nominal tickness of300 μm, is positioned and fastened on the cup by a proper flange. Thecup is overturned to put the liquid into contact with the polymer, andtransferred in a thermostated stove at the required temperature. A lightN₂ flow is directed on the free surface of the plaque. At prefixed timeintervals, the cup is transferred on a precision balance and weighed. Bydifference with the initial weight, the weight loss due to the flowingof the solvent permeated through the polymer, is calculated.

[0083] The result is expressed in g_(permeate)/(24 h·m². The results ofdifferent tests can be compared each other by normalizing them takinginto account the plaque thickness.

[0084] Therefore the final permeability coefficient is usually expressedin g_(permeate)·mm/(24 h·m²).

[0085] Method II

[0086] A phial having the capacity of about 5 cc, formed by the polymercompound of which one wishes to determine the permeability, is filledwith the tested liquid and then thermowelded so that it is hermeticallysealed. The phial is transferred in a dryer for 30 minutes and then in astove at the test temperature. After 300 hours the phial is taken awayfrom the stove and conditioned in the dryer at room temperature for 30minutes and then weighed.

[0087] The test result is expressed as variation per cent by weight(ΔP/P)×100 wherein P is the phial initial weight. This ratio representsthe fluid loss due to the permeation normalized for the total initialweight of the phial. The method precision is about 0.03%.

[0088] Determination of the Polymer Compound Swelling

[0089] The polymer compound swelling has been determined according toASTM D 471 by dipping the specimens in the tested fluid. Two tests havebeen carried out, at 100° C. and 80° C. respectively. The treatment timewas of 72 hours. The specimen swelling is expressed by the followingratio:$\frac{\left\lbrack {\left( {weight}_{{after}\quad {dipping}} \right) - \left( {weight}_{initial} \right)} \right\rbrack}{{weight}_{initial}} \times 100$

Example 1

[0090] Triboelectric Measurements of a Compound of the Invention ofFormula (I)

[0091] A fluid of the invention commercially known with the nameH-Galden® ZT130, having the following formula:

HCF₂O(CF₂CF₂O)₃(CF₂O)_(0.4)CF₂H

[0092] and the following chemico-physical properties: Boiling point  130° C. Pour point −115° C. Kinematic viscosity at 25° C. 0.89 cSt(8.9 · 10⁵ m²/s) Dielectric constant at 25° C. (at 1 KHz) 3.6 Dielectricrigidity (gap 2.54 mm) 37.9 kV

[0093] has been introduced in the tank of the above described equipmentand let circulate in the PTFE pipe for one hour. The charge decrease onthe pipe was 96%.

Example 2 (Comparative)

[0094] Triboelectric measurements on a perfluoropolyether compoundhaving the same boiling point of the fluid used in Example 1.

[0095] The perfluoropolyether compound, commercially known as Galden®HT135, was used, having formula:

CF₃O(CF₂CF(CF₃)O)₂(CF₂O)_(1.9)CF₃

[0096] and the following chemical-physical properties: Boiling point135° C. Pour point <−100° C. Kinematic viscosity at 25° C. 1 cStDielectric constant at 25° C. (at 1 KHz) 2.1 Dielectric rigidity (gap2.54 mm) 40 kV

[0097] The liquid has been introduced in the tank of the above describedequipment and let circulate in the PTFE pipe for some hours. After thefirst hour an increase of the electrostatic charges of about 8 timeswith respect to the initial value, and after 5 hours of about 16 times,was recorded on the PTFE pipe.

Example 3

[0098] Permeability measurements according to the Method I with a fluidof the invention using as polymer compound PVDF

[0099] A fluid commercially known with the name of H-Galden® ZT85 isused, having the following formula:

HCF₂O(CF₂CF₂O)_(1.8)(CF₂O)_(0.4)CF₂H

[0100] having boiling point of 85° C.

[0101] The plaque is formed by polymer compound PVDF MP20®. The test hasbeen carried out at the temperature of 40° C. The permeabilitycoefficient resulted of 0.3 g·mm/24 h·m².

Example 4 (Comparative)

[0102] Permeability measurements according to the method I with acomparative fluid by using the same polymer compound of Example 3.

[0103] Example 3 was repeated by using as a fluid a compoundcommercially known with the name HFE® 7200 having formula C₄F₉OC₂H₅,with boiling point of 78° C. The plaque was equal to that used inExample 3. The permeability coefficient resulted of 2.5 g·mm/24 h·m².

[0104] This Example shows that a hydrofluoroether fluid having in themolecule a perfluoroalkyl radical linked to a hydrogenated alkoxy groupshows a permeability value clearly higher than that of ahydrofluoroether according to the present invention having a comparableboiling point.

Example 5

[0105] Permeability measurements according to the method I using aworking fluid according to the present invention, using as polymercompound PFA.

[0106] The same hydrofluoroether of Example 3 is used as working fluid.

[0107] The plaque is formed by polymer compound TEFLON® PFA 350. Thetest has been carried out at the temperature of 40° C. The permeabilitycoefficient resulted of 1.5 g·mm/24 h·m².

Example 6 (Comparative)

[0108] Permeability measurements according to the method I with acomparative fluid, using the same polymer compound of Example 5.

[0109] Example 5 was repeated using as working fluid thehydrofluoroether compound of Example 4 (comparative), using a plaqueequal to that of Example 5. The permeability coefficient resulted of 3.1g·mm/24 h·m².

[0110] The above comments referred to the results obtained in Example 3and Example 4 (comparative) can be repeated.

Example 7

[0111] Permeability measurements according to the method II with a fluidof the invention, using as polymer compound polyethylene.

[0112] The same fluid used in Example 1 is used. The test was carriedout at the temperature of 60° C. The variation by weight of the fluid,due to permeation, calculated as above, is 1%.

Example 8 (Comparative)

[0113] Permeability measurements according to the method II with acomparative fluid, using the same polymer compound of Example 7.

[0114] Example 7 has been repeated using as fluid a compoundcommercially known with the name HFE® 7500 having formula C₇F₁₅OC₂H₅ andboiling point of 128° C.

[0115] The test has been carried out at the temperature of 60° C. Thevariation by weight of the fluid, due to permeation, calculated as aboveindicated, is 2%.

Example 9

[0116] Determination of the swelling of a polymer compound for gasketsmade by cured silicone rubber put into contact with a fluid according tothe present invention.

[0117] The fluid described in Example 1 (b.p. 130° C.) has been used,employing silicone rubber plaques having a nominal thickness of 0.8 mm.

[0118] The test temperature was of 100° C. The swelling percentage was4%.

Example 10 (Comparative)

[0119] Determination of the swelling of a polymer compound for gasketsmade by cured silicone rubber put into contact with a hydrofluoroetherfluid of the prior art.

[0120] Example 9 has been repeated using the fluid described in Example8 (comparative) having b.p. of 128° C.

[0121] The swelling percentage was 16%.

Example 11

[0122] Determination of the swelling of a polymer compound for gasketsmade by cured silicone rubber put into contact with a fluid according tothe present invention.

[0123] The fluid described in Example 3 was used, (b.p. 85° C.) usingsilicone rubber plaques having a nominal thickness of 0.8 mm.

[0124] The test temperature was 80° C. The swelling percentage was 8%.

Example 12 (Comparative)

[0125] Determination of the swelling of a polymer compound for gasketsmade by cured silicone rubber put into contact with a hydrofluoroetherfluid of the prior art.

[0126] Example 11 has been repeated using the fluid described in Example4 (comparative), having b.p. of 78° C.

[0127] The swelling percentage was 50%.

1. Use of one or more fluorinated liquids as dielectric working fluidsin plants or heat transfer circuits comprising parts formed by polymermaterial in contact with said fluids, said fluorinated liquids having:boiling point in the range 50° C.-250° C., preferably 70° C.-200° C.,formula R′-R_(f)-R  (I) wherein: R′ is —(O)_(n0)—C_(n)F_(2n)H, n beingan integer from 1 to 4, preferably 1 or 2; n0 is equal to 0, 1; R is:—C_(n)F_(2n)H, —C_(m)F_(2m+1), wherein: in the end groups R, R′ onefluorine atom is optionally substituted with one chlorine atom; n is asabove defined and m is an integer from 1 to 3; R_(f=) linear or branchedperfluoroalkylene from 2 to 12 carbon atoms, containing at least oneether oxygen atom; when R_(f) has said meaning n0 in R′ is preferablyequal to zero; perfluoropolyoxyalkylene comprising units statisticallydistributed along the chain, selected from the following: (CFXO) whereinX=F or CF₃; (CF₂(CF₂)_(d)O) wherein d is an integer comprised between 1and 3; (C₃F₆O); when R_(f) is perfluoropolyoxyalkylene n0 in R′ ispreferably equal to
 1. 2. Use according to claim 1, wherein the unit(C₃F₆O) in R_(f) has the following meanings: (CF₂CF(CF₃)O),(CF(CF₃)CF₂O).
 3. Use according to claims 1-2, wherein in formula (I) Ris a group selected from the following: —CF₂H, —CF₂CF₂H, —CFHCF₃.
 4. Useaccording to claims 1-3, wherein the compounds of formula (I), have anumber average molecular weight from 200 to
 800. 5. Use according toclaims 1-4, wherein when R_(f)=(per)fluoropolyether chain, n0 in R′=1,and R_(f) in R′- R_(f)-R has one of the following structures: 1)—(CF₂O)_(a)—(CF₂CF₂O)_(b)— when a is different from zero, then b/a iscomprised between 0.3 and 10, extremes included; when a is equal to zerob is an integer as defined below; R in formula (I)=—C_(n)F_(2n)H; 2)—(CF₂—(CF₂)_(z′)—CF₂O)_(b′)— wherein z′ is an integer equal to 1 or 2;b′ is as defined below; 3) —(C₃F₆O)_(r)—(C₂F₄O)_(b)—(CFL₀O)_(t)— L₀=—F,—CF₃; when b and t are different from zero r/b=0.5-2.0; (r+b)/t=10-30and all the units with r, b and t indexes are present; or b=t=0 and rsatisfy the proviso indicated below; or b=0 and r and t are differentfrom zero; a, b, b′, r, t, are integers, whose sum is such that thecompound of formula (I) has a boiling point in the above range.
 6. Useaccording to claims 1-5, wherein the compounds of formula (I) have thefollowing formulas: HCF₂O(CF₂CF₂O)_(1.8)(CF₂O)_(1.4)CF₂H;HCF₂O(CF₂CF₂O)₂(CF₂O)_(0.7)CF₂H; HCF₂O(CF₂CF₂O)₃(CF₂O)_(0.4)CF₂H;HCF₂O(CF₂CF₂O)₃(CF₂O)_(1.6)CF₂H; HCF₂O(CF₂CF₂O)₄(CF₂O)_(0.9)CF₂H;CF₃O(CF₂CF₂O)₂CF₂H; CF₃O(CF₂CF₂O)₂(CF₂O)CF₂H; CF₃O(CF₂CF(CF₃)O)₂CF₂H;CF₃O(CF₂CF(CF₃)O)₃CF₂H; CF₃O(C₃F₆O)₂(CF(CF₃)O)CF₂H;HCF₂CF₂O(CF₂CF₂O)CF₂CF₂H; HCF₂CF₂OCF₂C(CF₃)₂OCF₂CF₂CF2H;CF₃(CF₂)₅OCF₂CF₂H; CF₃(CF₂)₆OCF₂H; C₅F₁₁OC₅F₁₀H.
 7. Use according toclaim 6, wherein the compounds of formula (I) are the following:HCF₂O(CF₂CF₂O)₃(CF₂O)_(0.4)CF₂H; HCF₂O(CF₂CF₂O)_(1.8)(CF₂O)_(0.4)CF₂H.8. Use according to claims 1-7, wherein the fluorinated liquids areconstituted by mixtures of the compounds of formula (I).
 9. Useaccording to claims 1-8, wherein the plants or heat transfer circuitswherein the compounds of formula (I) or mixtures thereof are used,comprise parts formed by plastomeric and elastomeric polymer compounds,both fluorinated and hydrogenated.
 10. Use according to claim 9, whereinthe polymer compounds are formed by polymers or copolymers oftetrafluoroethylene and of vinylidene fluoride; polymers and copolymersof ethylene and propylene, EPDM, silicone rubbers.